Weather radars provide precipitation estimates with high spatial and temporal resolutions but with limited accuracy. A network of rain gauges can provide more accurate point-wise measurements but the spatial representativeness is limited. Rain gauge measurements are often combined with weather radar observations to improve quantitative precipitation estimates.
Evaluation of merging methods
Observations from the Wideumont radar and a dense rain gauge network of the Walloon region are used to estimate daily rainfall accumulations. Several radar-gauge merging methods with various degrees of complexity have been tested: from mean field bias correction to geostatistical merging techniques. Their relative performances are assessed through a comparison against daily measurements from the RMI climatological network.
Walloon Region with Wideumont radar (black square), SPW telemetric gauge network and RMI climatological gauge network.
A 4-year verification has been performed using several statistical quality parameters. It appears that the geostatistical merging methods perform best with the mean absolute error decreasing by 40% with respect to the original data. A mean field bias correction still achieves a reduction of 25%.
A seasonal analysis shows that the benefit of using radar observations is particularly significant during summer. The effect of the network density on the performance of the methods has also been investigated. The analysis reveals that the sensitivity is relatively high for the geostatistical methods but rather small for the simple methods. The geostatistical merging methods give the best results for all tested network densities and their relative benefit increases with the network density.
The results of the long-term evaluation have been used for the development of operational products.
Hourly precipitation accumulation maps are generated in the framework of a collaboration with the water management authorities of the Brussels region (SBGE) . The product makes use of observations from the Wideumont radar and SBGE network which includes 15 telemetric rain gauges.
Convective storm episode of 20 July 2009 over Brussels. Hourly precipitation accumulation from radar data corrected by a mean field bias.
Contact person for this topic: Edouard Goudenhoofdt